Detonator-sensitive assembled booster charges for use in blasting engineering and the use thereof

ABSTRACT

This invention relates to detonator-sensitive assembled booster charges for use in blasting engineering. The booster charge comprises nitroalkane and a cavity-forming agent.

This application is a continuation of U.S. patent application Ser. No.14/442,197, filed May 12, 2015, and published on Feb. 25, 2016, as2016-0052835 A1, which is a National Phase filing under 35 U.S.C. § 371of International Application No. PCT/EP2013/073658, filed Nov. 12, 2013,and published as WO 2014/076099-A2 on May 22, 2014, which claims benefitof priority from German Patent Application Serial No. DE 10 2012 110955.9, filed Nov. 14, 2012. The entire contents of each of the priorapplications are incorporated herein by reference in their entirety.

The invention concerns detonator-sensitive assembled booster charges foruse in blasting engineering.

Insensitive, non-toxic and inexpensive explosives, mostly based onammonium nitrate, are preferentially used in civil blastingapplications. In salt mining or tunnel driving, for example, so-calledpumping explosives are used in addition to the long familiar ANFO. Pumpexplosives are differentiated into emulsion explosives and suspensionexplosives (slurries, explosive slurries).

ANFO (Ammonium Nitrate Fuel, trade name e.g. ANDEX) is a mixture ofporous ammonium nitrate and mineral oil or diesel oil (fuel oil), whichis used in the mining industry as a safe-to-handle explosive.

In addition, if not sufficient for safe ignition, these explosivesrequire so-called primary explosives in conjunction withdetonator-sensitive assembled initiation charges (boosters, amplifiercharges or primers). Primary explosives can be found in commercialdetonators. Primary explosives are characterized by high sensitivity tofriction, shock, impact and heat. Mercury fulminate, for example, canalready be detonated by heating to 160° C. (detonating cord) or by a 2kg drop hammer falling from a height of 4 cm. Initial detonation withblasting caps was invented in 1862 by Alfred Nobel. Important primaryexplosives are mercury fulminate, lead azide, silver azide, silveracetylide, silver fulminate, diazodinitrophenol, lead picrate(trinitrophenol lead), lead styphnate (lead trinitroresorcinate),tetracene, nickel hydrazine nitrate (NHN), hexamethylene triperoxidediamine (HMTD), acetone peroxide (DADP, TATP or APEX),3-nitrobenzenediazonium perchlorate, mercury azides, tetraamine copper(II) chlorate (TACC) and copper acetylide.

Pressed cylindrical explosive devices made of tetryl, trinitrotoluene,phlegmatized (reduction of sensitivity) hexogen, pentaerythritoltetranitrate (PETN), picric acid and other explosives are usually usedas detonator-sensitive assembled booster charges, also referred to asinitial gain detonator or IG detonator. Common to all these substancesis a greater sensitivity to the initial pulse than that of the explosiveof the main charge (e.g. ANFO, cast TNT, powdery explosives). Primercartridges of gelatinized explosives are often used in rock blasting asan additional amplification charge to initiate the main charge ofpowdery explosives or emulsion explosives. The weight and the shape ofthe IG detonator are calculated so that, at detonation, a pulse isproduced that ensures the triggering of the detonation of the maincharge and the desired detonation behavior. The initiation of the IGdetonator is triggered by a blasting cap, an electric detonator or aNE-igniter (non-electric igniter).

The problem with the IG detonators used to date is that they eitherconsist of long term no longer available military explosives (pressedTNT, cast Composition B, etc.), or that classic primer cartridges madeof gelatinous explosives (dynamite successors on the basis of blastingoil) are used, which becomes problematic in the long term. Besides theincreased health hazard from nitric acid ester, the complicated andhazardous production and the associated high cost are a significantissue.

U.S. Pat. No. 3,902,933 A discloses an initial explosive charge fordetonation of nitromethane. The initial explosive charge is formed by apolyurethane foam containing dispersed microspheres. The microspherescan be hollow glass microspheres, resin beads, ceramic beads, etc.

Further disclosed, in U.S. Pat. No. 4,334,476 A, is an initial explosivecharge for granular or liquid explosives, with an interior channel tohold the ignition device, whereby the interior channel exhibits a smallwall thickness so as to improve the detonation. This ensures theseparation of the liquid explosive and the ignition device.

Finally, U.S. Pat. No. 3,797,392 A discloses microspheres, used for thesensitization of liquid explosives. These microspheres, such as hollowglass spheres, ceramic microspheres or silicon carbide, are dispersed inthe liquid explosive right away and subsequently ignited. The use ofopen-pored polyurethane foams is described as well.

Therefore, the task of the invention is to specify an IG detonator thatcan be used safely, is inexpensive and safe to manufacture, and can behandled with no risk to health.

The task is solved with a detonator-sensitive booster charge accordingto claim 1. Advantageous embodiments are specified in the dependentclaims.

According to the invention, a detonator-sensitive booster chargecomprising a mixture including a nitroalkane and a cavity-forming means,as well as a slot for an ignition device, is suggested.

Surprisingly, it was found that nitroalkanes are well-suited for use indetonator-sensitive booster charges.

Nitroalkanes can be activated chemically, e.g. by addition of amine,and/or mechanically via the creation of small hollow spaces orgas-filled cavities (foaming), i.e. they become detonator sensitive andbehave like volatile explosives. In order to maintain a uniformdistribution of the cavity formers, the addition of a thixotropic agentis indicated. Such mixtures are disclosed in U.S. Pat. No. 3,713,915.

Nitromethane mixtures, which are produced with commercially availablehollow glass microspheres (glass microballoons, GMB) and which detonateat more than 6000 m/s and are detonator-sensitive, are also known(Presles et al. Shock Waves, April 1995, Volume 4, Issue 6, p. 325-329).

In one embodiment of the invention, the detonator-sensitive boostercharge is made of a liquid-impermeable material. This prevents leakingof the nitroalkane.

In a further embodiment of the invention, the detonator-sensitivebooster charge exhibits a concave curvature arranged on the oppositeside of the slot for the ignition device. In the sense of the presentinvention, a concave curvature is a conical or hemispherical curvatureon the direction of the center of the booster charge. With the concavecurvature the effect of a hollow charge is achieved, which results in anincreased detonation velocity. The curvature causes the energy releasedby the detonation to be focused in this direction. For this reason thebooster charge is inserted with the concave curvature in the directionof the main charge. The advantageous design with concave curvaturesignificantly increases the effectiveness of the inventive boostercharge.

In a further embodiment of the invention, the concave curvature exhibitsa metallic coating. The metallic coating can be made of aluminum andapplied to the surface of the concave curvature by spraying, steaming oras a metallic film. The metallic coating of the concave curvatureaffects an intensifying initial pulse in a specified direction.

The concave curvature with a metallic coating is of particularimportance for achieving a high chemical implementation rate, in whichthe implementation process comes very close to the theoretical value.This significantly reduces the level of harmful substances in theborehole column charge for the commercial explosives to be activated.

In another embodiment of the invention, the ignition device is ablasting cap, a detonating cord or a non-electric detonator.

In a further embodiment of the invention, the detonator-sensitivebooster charge exhibits a suitable wall thickness. This ensures a secureignition transfer from the cap or the cord to the nitroalkane mixture.The wall thickness is dependent on the material of the wall as well asthe mixture used.

In a further embodiment of the invention, the nitroalkane is selectedfrom a group with 1 to 3 carbon atoms.

In a further embodiment of the invention, the nitroalkane isnitromethane.

In a further embodiment of the invention, the cavity-forming means isconfigured as a hollow glass microsphere.

In a further embodiment of the invention, the cavity-forming means isconfigured as a hollow glass microsphere with a grain size of 20-200 μm,preferably 40-150 μm, particularly preferred 80-120 μm.

In a further embodiment of the invention, the cavity-forming means isconfigured as a hollow glass microsphere with a grain size ofsubstantially 100 μm.

In a further embodiment of the invention, the mixture includes Aerosil.In this context Aerosil is a fumed silica.

In a further embodiment of the invention, the mixture exhibits 1.5-10weight %, preferably 3-8 weight %, particularly preferred 5-7 weight %Aerosil, 0.2-10 weight %, preferably 0.5-5 weight %, particularlypreferred 0.8-2 weight % hollow glass microspheres and 85-98.3 weight %,preferably 89-95, particularly preferred 91-93 weight % nitromethane.

In a further embodiment of the invention, the mixture exhibits 6.5weight % Aerosil, 1 weight % hollow glass microspheres with a grain sizeof substantially 100 μm and 92.5 weight % nitromethane.

In a further embodiment, the mixture also comprises at least oneoxygen-containing compound selected from the nitrates group to increasethe oxygen balance. In one design of the embodiment, theoxygen-containing compound is ammonium nitrate.

The use of the inventive detonator-sensitive booster charge is also thesubject matter of the invention.

The figure is a drawing of a non-limiting example of adetonator-sensitive booster charge as herein disclosed.

The inventive detonator-sensitive booster charges are used to initiatenon-detonator-sensitive commercial explosives, preferentially inboreholes on the surface and below ground, to initiate larger amplifiercharges and for direct use for special blasting (avalanches, ice etc.).In particular, the inventive detonator-sensitive booster charges areused for the initiation of explosives in mining applications and tunnelconstruction.

In doing so the inventive detonator-sensitive booster charges exhibitthe following advantages:

Detonation velocities of ca. 6000 m/s are achieved with the inventivedetonator-sensitive booster charges, allowing the detonation ofnon-detonator-sensitive explosives. Moreover, no nitroaromatics, whichare suspected to be carcinogenic, and no nitroesters, which arephysiologically problematic due to possible vasodilation, are formedwhen the detonator-sensitive booster charges are used. Health problemsamong users can thus be avoided. In addition, the inventively preferrednitroalkane nitromethane is an inexpensive product that, due to thegas-phase nitration of propane, is available for the long term—even whenrecycled military explosives become scarce.

Nitromethane is also not a classic explosive, which makes transport andstorage inexpensive, and is of storage class 3 (flammable liquids). Inaddition, nitromethane has low toxicity: LD50 oral rat: 940 mg/kg, WHC2.

It is also advantageous that, in the event of damage, the inventivedetonator-sensitive booster charges “deactivate” themselves by completevolatilization of the nitromethane into the air.

The inventive detonator-sensitive booster charges are designed to beabsolutely waterproof and temperature-resistant. There is no exudationof fluids. Thus, because there are no chemical reactions between themixture components, the inventive detonator-sensitive booster charges ina mixture with Aerosil and GMBs have a practically unlimited shelf life.

Moreover, the manufacturing of the inventive detonator-sensitive boostercharges invention does not require dangerous melting processes. Inaddition, no long waiting period is necessary after mixing of thecomponents, which is why manufacturing can be easily and safely (awayfrom people) automated.

It is also important that the components in the mixture are notexplosive materials, necessitating only minor storage and transportationcosts.

Preferred embodiments of the invention result from combinations of theclaims or individual features thereof.

In the following, the invention will be described in detail withreference to several design examples. The design examples are intendedto describe the invention without limiting it.

In one design example of the invention, pure ammonium nitrate and ANFO(in each case with 13 g of the inventive composition in a cylindricalbooster charge) with the following composition were brought to adetonative reaction: 6.5% Aerosil, 1% GMBs ca 100 μm, 92.5%nitromethane.

In the process, detonation velocities of ca. 4500 m/ were measured,which indicates adequate suitability of the mixture for the initiationof non-detonator-sensitive commercial explosives to initiate largeramplifier charges and for direct use for special blasting (avalanches,ice, etc.).

A non-limiting example of a detonator-sensitive booster charge as hereindisclosed is illustrated in the figure. The figure shows a detonatorsensitive booster charge 1, an ignition device 2, a mixture comprisingnitromethane and cavity forming means 3, and a concave curvature 4.

1-15. canceled
 16. A detonator-sensitive booster charge for use inblasting engineering comprising: a mixture comprising a nitromethane,fumed silica, and a cavity-forming means comprising a plurality ofhollow glass microspheres, and a receptacle for an ignition device,wherein the booster charge is configured so as to be waterproof andtemperature-resistant.
 17. The detonator-sensitive booster chargeaccording to claim 16, wherein the booster charge is made of aliquid-impermeable material.
 18. The detonator-sensitive booster chargeaccording to claim 17, wherein the booster charge exhibits a concavecurvature arranged on an opposite side of the receptacle for theignition device.
 19. The detonator-sensitive booster charge according toclaim 18, wherein the concave curvature comprises a metallic coating.20. The detonator-sensitive booster charge according to claim 16,wherein the ignition device comprises a blasting cap, a detonating cord,or a non-electric detonator.
 21. The detonator-sensitive booster chargeaccording to claim 16, wherein the hollow glass microsphere has a grainsize of 20-200 μm.
 22. The detonator-sensitive booster charge accordingto claim 18, wherein the mixture comprises between 85% by weight and98.3% by weight nitromethane, between 1.5% by weight and 10% by weightfumed silica, and between 0.2% by weight and 10% by weightcavity-forming means comprising a plurality of hollow glassmicrospheres.
 23. The detonator-sensitive booster charge according toclaim 17, wherein the mixture comprises 92.5% by weight nitromethane,6.5% by weight fumed silica, and 1% weight cavity-forming meanscomprising a plurality of hollow glass microspheres, wherein the hollowglass microspheres have a grain size of substantially 100 μm and. 24.The detonator-sensitive booster charge according to claim 16, furthercomprising an oxygen-containing compound selected from the nitratesgroup.
 25. The detonator-sensitive booster charge according to claim 21,wherein the hollow glass microspheres have a grain size of between40-150 μm.
 26. The detonator-sensitive booster charge according to claim21, wherein the hollow glass microspheres have a grain size of between80-120 μm.
 27. The detonator-sensitive booster charge according to claim22, wherein the mixture comprises between 85% by weight and 95% byweight nitromethane, between 3% by weight and 8% by weight fumed silica,and between 0.5% by weight and 5% by weight cavity-forming meanscomprising a plurality of hollow glass microspheres.
 28. Thedetonator-sensitive booster charge according to claim 27, wherein themixture comprises between 91% by weight and 93% by weight nitromethane,between 5% by weight and 7% by weight fumed silica, and between 0.8% byweight and 2% by weight cavity-forming means comprising a plurality ofhollow glass microspheres.